Well, it turns out that if you have an algorithm which works tremendously well for 98% of cases that it comes across, the remaining 2% of cases are inevitably a collection of the most bizarre input data that you can imagine.  The algorithm I am talking about is the iliac tracking which I essentially completed near the end of December.  For the past couple of weeks, I have been trying to find ways to solve the problems that arise with specific scans.  There are a couple of general categories of scans which cause problems.
The first is the setting of very low contrast in the vessel.  These are not as big of a problem as you might think.  In fact, the algorithm does a fairly good job of successfully tracking the vessels as long as there is some amount of contrast present.
The second problematic class of cases is when there are endovascular stents in place.  Again, this is not as much of an issue as you might think with the cases that I am working with.  At some point I will have to go back and write some dedicated code for analyzing the stents, but for now the salvage algorithms seem to pick up the pieces fairly well.
The last major class of scans is the surgical aorta where there is something like an aortobifem graft.  Those graft tend to arise almost perpendicular to the abdominal aorta where they are sewn on.  It is that abrupt change in direction that has caused the largest number of problems for my algorithm.  Some amount of smoothness to the vessel course and curvature is implicit in the ways that my tracking algorithms function.  At this point I am forced to allow the algorithm to complete tracking whatever vessel it has managed to track and now we go back and analyze the results and find where the rest of the tracking should start.  As you can imagine, this is nether a philosophically satisfying or technically simple task.  Fortunately, this give me a chance to fine tune my skills at probing vessels for small branches since one of the next steps is going to be isolating the visceral artery ostia.
Well, enough talk... time to get some coding done.